United States
Department
of Agriculture
Forest Service
Pacific Southwest
Research Station
http://www.psw.fs.fed.us/
Research Paper
PSW-RP-239
Diversity, Density, and Development of
Early Vegetation in a Small Clear-cut
Environment
Philip M. McDonald
Publisher:
Albany, California
Mailing address:
PO Box 245, Berkeley CA
94701-0245
510 559-6300
http://www.psw.fs.fed.us
September 1999
Pacific Southwest Research Station
Forest Service
U.S. Department of Agriculture
Abstract
McDonald, Philip M. 1999. Diversity, density, and development of early vegetation in a small clear-cut
environment. Res. Paper PSW-RP-239. Albany, CA: Pacific Southwest Research Station, Forest Service,
U.S. Department of Agriculture; 22 p.
On a high quality site in northern California, frequency, density, foliar cover, and height were measured on
every plant species present in an 8-acre clear-cut opening each year from 1976 through 1980. Plant species
numbered 71, although no more than 62 were present during a given year. Categories of vegetation with the
most plants per acre initially were shrubs, annuals and biennials, and ferns; at the end of the study the
categories were annuals and biennials, graminoids, and shrubs. At the beginning of the study, bracken fern
provided the highest amount of foliar cover, whereas 5 years later shrubs and annuals and biennials provided
the most cover. Hardwoods and graminoids were the tallest categories of vegetation. At the study’s end
density was 112,408 plants per acre, foliar cover was 17,433 ft2 per acre and the tallest plants were 3.5 to 4.9
feet tall. Implications for future species development, plant succession, and community composition are
presented.
Retrieval Terms: natural vegetation, northern California, plant community, plant species development, small
forest opening
The Author
Philip M. McDonald is a research forester assigned to the Pacific Southwest Research Station’s Forest Growth
and Development Research Unit at the Silviculture Laboratory, 2400 Washington Ave., Redding, CA 96001.
Diversity, Density, and Development of
Early Vegetation in a Small Clear-cut
Environment
Philip M. McDonald
Contents
Pacific Southwest
Research Station
In Brief . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ii
USDA Forest Service
Research Paper
PSW-RP-239
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Species and Site Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Treatment, Measurement, and Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Sampling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2
2
4
4
Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Plant Diversity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Individual Species . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Categories of Species . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
The Plant Community . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
Discussion and Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
September 1999
In Brief…
McDonald, Philip M. 1999. Diversity, density, and development of early vegetation in a small clear-cut
environment. Res. Paper PSW-RP-239. Albany, CA: Pacific Southwest Research Station, Forest
Service, U.S. Department of Agriculture; 22 p.
Retrieval Terms: natural vegetation, northern California, plant community dynamics, plant species
development, small forest opening
T
he forest ecosystem manager of the near future will need a tremendous amount of data. An
inescapable fact is that an ecosystem cannot be managed without inventory data on as many
plants, animals, insects, and genes as possible. Disturbance, either from nature or humans, is
inevitable, and key questions include: how do ecosystems change and develop after a disturbance, and
what are the long-term implications of such changes? Unfortunately, data to answer these questions
are lacking or fragmented.
The primary focus of this 5-year (1976-1980) study was to record every plant species that was
present in a small composite clearing on a high quality site in northern California and to measure the
height and width of each over time. In addition, the five major regeneration strategies were examined
to determine which were operative and to link species presence and development to them. Change was
a major interest. The presence or absence of a species, the gain or loss in density, an elongation or
decline in height—all were observed with interest. Further, the ascendence or decline of various
categories of vegetation (conifers, hardwoods, shrubs, annuals and biennials, perennials, graminoids
[grasses and sedges], and bracken fern) were monitored with vigor.
The fact that this was a high quality site is important. To the vegetation, this means plentiful
rainfall, warm temperatures, and a long growing season. It also means deep soil, with inherent
capability to catch and hold critical moisture. Further, it suggests that the nutrient pool is large and
that critical nutrients are available as long as soil moisture is adequate. More specifically, it means that
the land can support many plants of many species with a potential for rapid growth. However, the long,
hot, rainless summers of the Mediterranean climate guarantee that when the soil moisture is gone,
there is no more. Soil moisture is the limiting factor to establishment, growth, and survival. Plants
must adapt a strategy of growing as fast as they can as soon as they can. Then they either die or find a
way to endure months of high temperatures, searing winds, and minimum amounts of soil moisture.
Seventy-one species were present during this study. The number of plant species present after
one growing season was 47 and after five seasons was 62. Nine species had disappeared by the study’s
end, only to be replaced by many new species, mostly perennials. Plant density reflected the high
quality site with 24,860 plants per acre present initially and 112,408 per acre after five growing
seasons. Foliar cover increased from 950 to 17,433 ft2 per acre during the study, and the tallest plants
were 3.5 to 4.9 feet in height. In general, the annuals and biennials were major contributors to density,
shrubs to foliar cover, and the graminoids to height. For a given descriptor (density, cover, height),
and specific year, many species excelled at least once. The most consistent ratings, however, were
achieved by bracken fern, which ranked among the top four species each year in terms of density and
foliar cover, and tanoak, which was present among the top four species in terms of height for 4 of the 5
years in the study.
All five regeneration strategies were used: rapid growth above ground was characterized by the
root crown sprouts of the hardwoods and shrubs, rapid growth below ground by bracken fern, the
seedling bank by tanoak and at least one perennial, windblown seeds by many annuals and biennials as
well as graminoids and some perennials, and finally the seedbank in the soil by many shrubs and some
annuals and perennials.
Some early trends in the composition of the future plant community can be deciphered. Chief
among them were that initial species with tall life forms and either established root systems or
capability to rapidly develop downward thrusting systems probably will do well. Hardwoods and
shrubs have this capability and will dominate in the future plant community. The conifers, chiefly
ponderosa pine, will also be present in the future community, but scattered as individual trees and in
small aggregations. Shade-enduring perennials and bracken fern will be present in the understory of
the future plant community; they also tend to develop deep and extensive root systems. The more
shallow-rooted annuals and graminoids are likely to be represented only by small numbers in small
openings where site resources are more readily available.
ii
USDA Forest Service Res. Paper PSW-RP-239. 1999.
Introduction
A
s ecosystem management and the enhancement of forest health become applied to Federal forest
land (Dombeck 1997, Salwasser 1992, Thomas 1994), information on the past, present, and
future plant community will be invaluable. Small openings in the landscape that are created by
wildfire, insect outbreak, or logging are commonplace, and knowledge is especially needed about
them. Merchantable stems in these areas often are harvested, the slash disposed of, and the ground
prepared for natural seeding or planting of desirable species.
Soil surfaces in these areas often are bare and temporarily devoid of most plants and animals.
Available site resources, however, are high because large quantities of organic material are incorporated
into the soil through harvesting and site preparation, and large amounts of moisture are absorbed by
this organic matter. Warm temperatures and added moisture cause a rapid buildup of microorganisms
that decompose organic material and liberate nutrients. Such nutrients, particularly nitrogen, increase
on productive sites during the first year or two after site preparation and then decline precipitously
(Smethhurst and Nambiar 1990).
In this fertile, but unstable and rapidly changing environment, the early plant community is
dynamic—increasing rapidly in number of species and number of plants, but changing as plants of
some species become numerous and those of other species decline. In productive environments,
vegetative regrowth originates from five regeneration strategies: rapid growth above ground (as from
sprouting hardwoods), rapid growth below ground (as from rhizomatous species), buried seedbanks
in the soil (many shrub species), seedling banks (shade tolerant species), and windblown seeds (many
annual species) (Grime 1979). In addition to the regeneration strategies, with their inherent
considerations of plant morphology, structure, and propagule dispersion, many other factors influence
plant location, density, and development in small openings on productive sites. These include slope
and aspect, past community makeup, and dominance potential of the various species.
Secondary plant succession, which is concerned with the development of vegetation on
temporarily-bare soil, was once thought of as primarily an orderly process (Clements 1916, Odum
1969). The first category of plants to become established after the soil was bared were the annuals,
followed by the herbaceous perennials, then the shrubs, and eventually the trees. This sequence or set
of stages was based on the precept that each category of vegetation prepared the way for the next stage
through environmental modification. However, Egler (1954) suggested that succession was not
necessarily an orderly or predictable process. Rather, the ensuing plant community developed from
the propagules (seeds, rhizomes) initially present in the area. Margalef (1963) noted that the
composition of early (pioneer) communities was determined by chance arrival during the initial period
when competition was low. In this study, plants from buried seeds, rhizomes, and sprouts were already
present and composition was hardly random. The impasse of orderly or random processes could be
resolved by assuming that the future composition of many forest plant communities derives from a
combination of both.
What is the process of plant succession in small openings surrounded by trees? How can it be
determined when the very species in these openings are largely unknown? McDonald and others
(1996) noted a major weakness when beginning ecosystem management on forested or formerly
forested land: “very little is known about the shrubs, forbs, and grasses in the community” (p. 1).
Gordon (1979) recommended that foresters begin to build a database for vegetation that is expected in
specific areas. Wagner and Zasada (1991) stated that forest managers across North America need to
consider the potential effect of noncrop vegetation on nearly every acre of newly forested land. These,
of course, are the currently uneconomic (noncrop) species as opposed to the “valuable” (economic)
conifers. O’Hara and others (1994) suggested that future forestry must embrace a mix of commercially
valuable and nonvaluable species, and Rietveld (1992) noted an increased demand for diverse tree and
shrub nursery stock, especially for species that provide food and shelter for wildlife.
The major objectives of this study were to ascertain the species composition of an early plant
community in a small clear-cutting in the northern Sierra Nevada and to gain knowledge on early
successional trends. More specific objectives were to list every species that was present in the clearing
each year for 5 years after site preparation, and to determine each species’ density and development,
both alone and in such categories as conifers, hardwoods, shrubs, annuals and biennials, perennials,
graminoids, and bracken fern. A second objective was to determine density and developmental trends
in each of these categories.
USDA Forest Service Res. Paper PSW-RP-239. 1999.
1
Methods
Species and Site Characteristics
The study was located on the Challenge Experimental Forest in north central California (Yuba County,
T19N, R7E MDM, Section 29). Site quality is high and the dominant species, ponderosa pine (Pinus
ponderosa Dougl. ex Laws. var. ponderosa), will average about 95 feet in height in 50 years (Powers
and Oliver 1978). Other tree species scattered over the Forest are coast Douglas-fir (Pseudotsuga
menziesii [Mirb.] Franco), sugar pine (Pinus lambertiana Dougl.), California white fir (Abies concolor
var. lowiana [Gord.] Lemm.), and incense-cedar (Libocedrus decurrens Torr.). Scientific and common
names of trees are from Little (1979), scientific names of all vegetation other than trees is from
Hickman (1993), and common names and plant symbols are from the U.S. Department of Agriculture
(1994). Hardwoods, principally California black oak (Quercus kelloggii Newb.), (plant symbol Quke),
tanoak (Lithocarpus densiflorus [Hook. & Arn.] Rehd.), (plant symbol Lide3), and Pacific madrone
(Arbutus menziesii Pursh) (Arme) (table 1), are present throughout as individual trees, clumps, or
groves. In terms of ecological subregions of California, the area corresponds to section M261E Sierra
Nevada and the granitic and metamorphic hills subsection (U.S. Department of Agriculture 1997).
Table 11—Scientific names, symbols, and common names of plant species in a composite clearcutting, Challenge Experimental Forest,
1976-1980
Vegetation
category
Libocedrus decurrens
Pseudotuga menziesii
var. menziesii
Pinus ponderosa
var. ponderosa
Hardwoods
Plant
symbol
Common
name
Lide
Incense-cedar
PsmeM
Coast Douglas-fir
PipoP
Ponderosa pine
Arbutus menziesii
Lithocarpus densiflorus
Quercus chrysolepis
Quercus kelloggii
Arme
Lide3
Quch2
Quke
Pacific madrone
Tanoak
Canyon live oak
California black oak
Shrubs
Arctostaphylos mewukka
Arctostaphylos viscida
Baccharis pilularis
Ceanothus lemmonii
Ceanothus prostratus
Chamaebatia foliolosa
Garrya fremontii
Haplopappus linearifolius
Ribes roezlii
Rosa gymnocarpa
Rubus glaucifolius
Toxicodendron diversilobum
Vitis californica
Arme3
Arvi4
Bapi
Cele
Cepr
Chfo
Gafr
Hali5
Riro
Rogy
Rugl
Todi
Vica5
Indian manzanita
Whiteleaf manzanita
Coyote brush
Lemmon’s ceanothus
Squawcarpet
Sierran mountain misery
Bearbrush
Ericameria linearifolia
Sierran gooseberry
Dwarf rose
Smoothleaf raspberry
Pacific poison oak
California wild grape
Annuals and
biennials
Cirsium vulgare
Clarkia rhomboidea
Conyza canadensis
Collomia heterophylla
Epilobium paniculatum
Eremocarpus setigerus
Galium aparine
Gnaphalium luteo-album
Hypochaeris glabra
Lactuca serriola
Lotus denticulatus
Lotus humistratus
Lotus purshianus
Madia gracilis
Mimulus torreyi
Civu
Clrh
Coca5
Cohe2
Eppa2
Erse3
Gaap2
Gnlu
Hygl2
Lase
Lode
Lohu2
Lopu3
Magr3
Mito
Bull thistle
Diamond fairyfan
Canadian horseweed
Variableleaf mtn. trumpet
Conifers
2
Scientific
name
Turkey mullein
Stickywilly
Jersey cudweed
Smooth catsear
Prickly lettuce
Riverbar birdfoot trefoil
Foothill deervetch
Grassy tarweed
Torrey’s monkeyflower
continues
USDA Forest Service Res. Paper PSW-RP-239. 1999.
Trees on the Experimental Forest larger than 3.5 inches in diameter at breast height (d.b.h.)
number more than 245 per acre and the average acre contains about 270 ft2/acre of basal area. The
previous forest was logged (at least for the largest and best trees) from about 1860 through 1890
(McDonald and Lahore 1984). Thus, logging and inevitable fire caused the current forest to be a mosaic
of even-aged, second-growth stands, with the oldest dominant and codominant trees being more than
100 years and averaging about 140 feet tall. Trees 170 feet and taller at the same age are not unusual.
Trees in the dominant and codominant crown classes on the Experimental Forest average about
35 per acre, 70 percent of which are ponderosa pines. In general, many trees of the more shade-tolerant
species (Douglas-fir, California white fir, incense-cedar, sugar pine, and tanoak) are younger, reflecting
a decreasing incidence of fire in the area. Greenleaf manzanita (Arvi4), deerbrush (Cein3), and western
bracken fern (Ptaq) are common on the Forest and often become abundant (table 1). Poison oak (Todi)
is ubiquitous and abundant, and grows equally well in sun and shade environments.
Herbivores, chiefly deer (Odocoileus spp.), woodrats (Neotoma spp.), and deer mice (Peromyscus
maniculatus), are plentiful throughout the Experimental Forest.
Summers on the Forest are hot and dry; winters cool and moist. The average midsummer
maximum temperature, based on 43 years of record, is 90 °F; the midwinter minimum is 30 °F. The
Table 11, continued
Vegetation
category
Scientific
name
Plant
symbol
Common
name
Annuals
and
biennials
Sonchus asper
Stephanomeria virgata
Tragopogon dubius
Trifolium ciliolatum
Vicia americana
Viola lobata
Soas
Stvi2
Trdu
Trci
Viam
Vilo2
Spiny sowthistle
Rod wirelettuce
Yellow salsify
Foothill clover
American vetch
Moosehorn violet
Perennials
Agoseris grandiflora
Apocynum pumilum
Aster radulinus
Campanula prenanthoides
Convolvulus aridus
Dichelostemma capitatum
Eriophyllum lanatum
Fragaria vesca
Galium bolanderi
Horkelia tridentata
Hypericum concinnum
Hypochaeris radicata
Iris hartwegii
Osmorhiza chilensis
Polygala cornuta
Potentilla glandulosa
Sanicula graveolens
Sidalcea malvaeflora
Tauschia kelloggii
Trientalis latifolia
Unknown rosette
Aggr
Appu
Asra
Capr15
Coar11
Dica14
Erla6
Frve
Gabo
Hotr
Hyco3
Hyra3
Irha
Osch
Poco4
Pogl9
Sagr5
Sima2
Take
Trla6
Unkn
Bigflower agoseris
Bromus (unknown)
Bromus orcuttianus
Carex (unknown)
Elymus glaucus
Festuca myuros
Festuca occidentalis
Sitanion hystrix
Brsp
Bror2
Casp
Elgl
Femy2
Feoc
Sihy
Pteridium aquilinum
var. pubescens
Ptaq
Graminoids
Bracken fern
USDA Forest Service Res. Paper PSW-RP-239. 1999.
Roughleaf aster
Bluedicks
Woolly eriophyllum
Woodland strawberry
Bolander’s bedstraw
Threetooth honeydew
Goldwire
Hairy catsear
Rainbow iris
Sierran milkwort
Gland cinquefoil
Northern sanicle
Dwarf checkermallow
Kellogg’s umbrellawort
Orcutt’s brome
Blue wildrye
Western fescue
Western bracken fern
3
growing season is about 200 days. Average annual precipitation is 68 inches with 94 percent falling
between October and May. Soil moisture is the limiting factor and drought the primary cause of
mortality for most plants. The Aiken soil grades from loam to clay-loam texture with depth, and is
deep, moderately well drained, and quite fertile. The study area, located at the 2,750-foot elevation,
faces southwest and has a 20 percent slope.
Treatment, Measurement, and Analysis
Merchantable trees were harvested in two small clear-cuttings in 1975, and slash and unmerchantable
trees were piled with a bulldozer in windrows and burned in the fall (fig. 1). Very little soil was placed
in the windrows. The clear-cuttings were 8.0 and 7.75 acres in size and about one-fourth of a mile
apart. Their soil, slope, aspect, and vegetation were representative of much of the Experimental Forest.
The two clear-cuttings were similar in every respect with one exception—most abundant shrub species.
In spring 1976, large numbers of whiteleaf manzanita (Arvi4) seedlings were present in one opening;
deerbrush (Cein3) seedlings in the other. Although not a trace of either species remained above
ground, large numbers of both species from dormant, but viable, seeds in the soil were expected in
each opening. The difference between openings was not anticipated. However, as noted by Sousa
(1984) and others, the environment within a patch cleared by disturbance is seldom, if ever,
homogeneous. Different microsites are inevitable and slightly different plant communities will become
present in each because of the adaptation of particular colonists to each. Because the overall
geographical features, soil, and vegetation were similar, data from the two openings were combined as
a composite to more closely represent this environment on the Experimental Forest.
Sampling
Sampling took place in the fall along three randomly selected diagonal transects in each opening that
roughly represented the top, middle, and bottom of each. Because the opening boundaries were
irregular, the length of the transects varied. Beginning and ending points of each transect were clearly
marked. Ten sampling locations were evenly distributed along each and determined by pacing. Sample
locations included the edge environment within 10 feet of the forest, but not burned windrows or
riparian vegetation in ephemeral stream channels near the bottom of the openings. Each location
became the center of a circular milacre (0.001 acre) plot. These were not permanently marked, and
thus the location of the plots varied slightly each year.
All vegetation was measured on each plot each year from 1976 through 1980. Years of extreme
drought were 1976 and 1977; 1978 was extremely wet, and 1979 and 1980 were about normal. Each
plant species was sampled for density, foliar cover, and height. Density was defined as the number of
Figure 1—A portion of the study
area on the Challenge Experimental
Forest in 1976. Close examination
shows a few small plants scattered
throughout the opening.
FPO
(for position only)
4
USDA Forest Service Res. Paper PSW-RP-239. 1999.
plants on each milacre plot expanded to a per-acre basis. Foliar cover was an estimate of the sum of
shadows that would be cast by leaves and stems of individual species expressed as a percentage of the
land surface (Daubenmire 1968). It is an expression of horizontal development. For each species,
amounts greater than 0.5 ft2 were recorded to the nearest 1.0 ft2 and less than this value as a trace (T). If
a plant leaned into the milacre and had at least a square foot of foliar cover in it, it was given a density
value of one plant. Plant height was denoted as “average dominant” and defined as the average of the
three tallest stems measured from mean groundline to bud. The height of an outward leaning plant was
recorded where it crossed the plot boundary. Frequency also was determined to provide an estimate of
species distribution within the opening. It was defined as the number of plots having one or more
plants of a given species divided by the total number of plots and expressed as a percent.
Results
Plant Diversity
A total of 71 plant species was found during the 5-year study (table 1), although no more than 62 species
were present during a given year (table 2). At the beginning of the study, the 45 species in the plant
community consisted of 0 conifer seedlings; 3 hardwoods from both root-crowns and seeds, 11 shrubs,
mostly from buried seeds; 15 annuals and biennials, all from seeds; 15 perennials, almost all from seeds;
2 graminoids (grasses and sedges), from seeds; and bracken fern, from rhizomes. At the end of the
study, the 62 species in the plant community consisted of 3 conifers, 2 hardwoods, 12 shrubs, 20
annuals and biennials, 18 perennials, 6 graminoids, and bracken fern (table 2; fig. 2). All categories of
vegetation increased, except hardwoods and fern, for an overall gain in diversity of 32 percent.
Table 22—Plant species diversity by vegetation category in a composite clearcutting, Challenge Experimental Forest, 1976-1980
Year
Conifers
Hardwoods
Shrubs
Annuals
Perennials
Graminoids
Fern
2
7
7
6
6
1
1
1
1
1
Total
Number of species
1976
1977
1978
1979
1980
0
3
3
3
3
3
2
3
2
2
11
12
11
12
12
15
16
18
16
20
15
12
14
15
18
47
53
57
55
62
Figure 2—At the end of the study
in 1980, the land was rapidly becoming
clothed with many plants from several
categories of vegetation, Challenge
Experimental Forest, 1980.
FPO
(for position only)
USDA Forest Service Res. Paper PSW-RP-239. 1999.
5
Individual Species
The vast majority of species became established early and persisted throughout the study period.
Several species, however, invaded early, were present for 1 to 3 years, and then disappeared. These
included Pacific madrone (Arme), bearbrush (Gafr), turkey mullein (Erse3), threetooth honeydew
(Hotr), canyon live oak (Quch2), northern sanicle (Sagr5), and Sitanian hystrix (Sihy) (table 3). They
represented almost all the vegetation categories in the study. Other species invaded later in the study.
Notable were coyote brush (Bapi), Convolvulus aridus (Coar11), woolly eriophyllum (Erla6), Bolander’s
bedstraw (Gabo), Jersey cudweed (Gnlu), goldwire (Hyco3), Osmorhiza chilensis (Osch), and yellow
salsify (Trdu), which, with one exception, were perennials.
Descriptive characteristics such as frequency, density, foliar cover, and height of the 71 plant
species portray the distribution, density, and development trends of individual species over the 5-year
study (table 3). Together, they encompass a wide variety of density and developmental trends, reactions
to competition, and adaptations to micro-environments. Strategies to dominate in some way at key
times also were observed. When the top four species in each descriptive characteristics class (density,
cover, height) were ranked, their regeneration and development strategies became more clear (table 4).
The first year after site preparation (1976), species like tanoak (Lide3), western bracken fern (Ptaq),
and Pacific poison oak (Todi), which derived energy from parent root systems, dominated in terms of
density and horizontal development (foliar cover). The second year (1977) was characterized by the
addition of annuals like bull thistle (Civu) and American vetch (Viam) and shrubs like whiteleaf
manzanita (Arvi4) and deerbrush (Cein3) that originated mostly from windblown seeds or from
dormant seeds in the soil. Year 3 (1978) was characterized by annuals like Civu, prickly lettuce (Lase),
and American vetch that originated mostly from newly produced seeds, and shrubs such as deerbrush
and whiteleaf manzanita that were developing rapidly. Species of note in year 4 (1979) were additional
annuals like smooth catsear (Hygl2) and riverbar birdfoot trefoil (Lode) along with the above shrubs
and western bracken fern (Ptaq). In year 5 (1980), density and cover were divided among most of the
species in year 4 plus blue wildrye (Elgl) and tanoak (Lide3). Of particular note was western bracken
fern, which was present among the top four species in both density and cover every year of the study.
This was the only species to do this.
Table 3—
3—Characteristics of individual species as they regenerated and developed during the study period, Challenge Experimental Forest,
1976-1980
Vegetation
category
Species
abbrev.
Year
Freq.
Density
Cover
Pct
Plants/acre
Value
SE
Height
Ft2/acre
Value
SE
Ft
Value
SE
Cade
1976
1977
1978
1979
1980
5
2
3
2
67
17
33
17
33
0
0
0
T
T
T
T
0
0
0
0
0.2
0.5
0.5
0.6
0.1
.0
0.4
.0
PsmeM
1976
1977
1978
1979
1980
2
3
3
5
17
33
33
50
0
0
0
0
T
T
T
T
0
0
0
0
0.2
0.6
0.4
0.6
.0
.0
0.2
0.4
PipoP
1976
1977
1978
1979
1980
25
33
35
22
467
483
433
350
29
15
10
21
T
17
67
33
0
0
0
0
0.2
0.3
0.7
1.0
0.1
0.1
0.2
0.3
Hardwoods Arme
1976
1977
1978
1979
1980
2
2
-
33
17
-
0
0
-
T
T
-
0
0
-
0.3
1.4
-
0
0
-
Conifers
continues
6
USDA Forest Service Res. Paper PSW-RP-239. 1999.
Table 33, continued
Vegetation
category
Species
abbrev.
Hardwoods Lide3
Freq.
Density
Cover
Pct
Plants/acre
Value
SE
Value
Height
Ft2/acre
SE
Ft
Value
SE
1976
1977
1978
1979
1980
1
22
17
17
25
210
233
183
217
350
10
6
10
15
16
90
217
217
783
900
2
2
6
145
117
1.4
2.6
2.0
4.8
4.9
0.2
0.3
0.4
0.5
0.6
1976
1977
1978
1979
1980
1
-
10
-
0
-
10
-
0
-
0.4
-
-
Quke
1976
1977
1978
1979
1980
4
10
3
5
10
40
150
83
100
100
0
22
150
100
0
T
100
T
17
168
0
100
0
0
233
0.4
1.5
0.5
0.7
2.2
0.1
0.4
0.1
0.3
1.0
Arme1
1976
1977
1978
1979
1980
2
3
2
5
3
17
17
17
33
33
0
0
0
0
0
T
T
T
33
T
0
0
0
0
0
0.1
0.1
0.1
1.8
0.3
.0
.0
.0
0.1
0.1
Arvi4
1976
1977
1978
1979
1980
41
50
58
70
65
1,680
3,517
2,917
3,533
4,467
100
243
142
142
146
70
617
1,383
2,083
4,183
0
51
73
16
153
0.3
0.7
1.2
1.3
2.4
0.1
0.1
0.1
0.2
0.2
Bapi
1976
1977
1978
1979
1980
2
17
0
T
0
3.2
-
Cein3
1976
1977
1978
1979
1980
60
63
63
72
67
2,960
3,150
3,783
3,000
2,617
550
580
125
46
47
T
717
1,850
4,100
4,033
0
20
68
114
106
0.2
1.2
1.4
2.3
3.4
0.1
0.1
0.1
0.2
0.4
Cele
1976
1977
1978
1979
1980
9
10
7
17
8
360
533
417
1,250
683
138
219
214
225
553
10
100
150
800
583
0
58
100
134
585
0.2
0.5
0.7
0.9
1.2
0.1
0.1
0.1
0.1
0.4
Cepr
1976
1977
1978
1979
1980
15
17
23
15
22
180
300
400
183
467
14
33
18
15
44
T
50
150
100
283
0
0
13
20
51
0.1
0.2
0.2
0.2
0.2
0.1
0.1
0.1
0.1
0.1
Chfo
1976
1977
1978
1979
1980
16
13
18
27
22
630
800
750
2,517
2,267
73
243
118
215
301
80
167
117
550
283
14
87
24
68
48
0.5
0.5
0.5
0.8
0.7
0.1
0.1
0.1
0.1
0.1
Gafr
1976
1977
1978
1979
1980
9
13
-
140
200
-
29
38
-
T
17
-
0
0
-
0.2
0.4
-
0.1
0.1
-
Quch2
Shrubs
Year
.0
.0
continues
USDA Forest Service Res. Paper PSW-RP-239. 1999.
7
Table 33, continued
Vegetation
category
Shrubs
Annuals
and
biennials
Species
abbrev.
Year
Freq.
Density
Cover
Pct
Plants/acre
Value
SE
Value
Height
Ft2/acre
SE
Ft
Value
SE
Hali5
1976
1977
1978
1979
1980
3
2
5
33
17
67
0
0
33
17
T
33
0
0
0
1.3
0.7
1.7
0.7
.0
0.4
Riro
1976
1977
1978
1979
1980
7
2
5
3
5
80
17
50
33
67
14
0
0
0
33
T
T
T
T
100
0
0
0
0
0
0.4
0.3
0.7
0.4
2.7
0.1
.0
0.1
0.4
0.4
Rogy
1976
1977
1978
1979
1980
14
10
17
12
13
430
417
1,133
367
350
60
91
255
116
56
30
83
67
33
T
0
67
100
T
0
0.4
0.6
0.5
0.7
0.6
0.1
0.1
0.1
0.1
0.1
Rugl
1976
1977
1978
1979
1980
29
20
32
27
30
430
483
817
500
583
38
61
82
39
22
30
117
167
217
200
0
48
11
75
24
0.3
0.6
0.6
0.4
0.8
0.1
0.3
0.1
0.1
0.1
Todi
1976
1977
1978
1979
1980
65
63
48
65
63
2,810
3,083
1,767
2,567
2,733
440
86
48
54
72
90
500
100
500
483
18
16
0
22
22
0.4
0.8
0.7
0.8
1.5
0.2
0.1
0.1
0.1
0.2
Vica5
1976
1977
1978
1979
1980
2
2
-
17
17
-
0
0
-
T
T
-
0
0
-
0.5
0.4
-
-
Civu
1976
1977
1978
1979
1980
49
88
95
70
62
1,860
20,367
13,583
3,467
4,017
67
367
216
73
55
110
1,833
2,467
467
267
43
41
66
21
27
0.6
1.5
1.7
1.6
1.6
0.2
0.1
0.2
0.1
0.1
Clrh
1976
1977
1978
1979
1980
2
3
3
0
933
750
0
999
250
T
33
100
0
0
200
1.0
1.5
2.5
0.4
0.5
0.5
Coca5
1976
1977
1978
1979
1980
3
7
3
7
50
67
50
1,083
50
0
50
441
17
T
T
17
0
0
0
0
2.8
1.9
1.1
0.7
1.0
0.6
0.2
0.4
Cohe2
1976
1977
1978
1979
1980
1
8
17
10
90
950
2,183
817
0
229
244
539
T
T
83
T
0
0
67
0
0.3
0.3
0.4
0.3
.0
0.1
0.1
0.1
Eppa2
1976
1977
1978
1979
1980
3
13
20
42
100
717
600
3,500
0
266
81
244
T
50
T
67
0
50
0
0
1.8
2.1
1.4
1.7
0.7
0.3
0.1
0.2
.0
.0
-
continues
8
USDA Forest Service Res. Paper PSW-RP-239. 1999.
Table 33, continued
Vegetation
category
Annuals
and
biennials
Species
abbrev.
Year
Freq.
Density
Cover
Pct
Plants/acre
Value
SE
Value
Height
Ft2/acre
SE
Ft
Value
SE
Erse3
1976
1977
1978
1979
1980
3
2
2
-
30
183
183
-
0
0
0
-
T
T
T
-
0
0
0
-
0.1
0.3
0.1
-
0.1
.0
.0
-
Gaap2
1976
1977
1978
1979
1980
2
2
17
17
0
0
T
T
0
0
0.5
3.1
-
Gnlu
1976
1977
1978
1979
1980
12
17
15
133
533
317
14
118
75
17
67
67
0
33
33
0.3
1.6
1.8
0.2
0.3
0.4
Hygl2
1976
1977
1978
1979
1980
11
13
53
38
47
180
183
2,833
4,600
17,367
28
38
106
281
912
T
17
183
250
783
0
0
31
24
72
0.1
0.9
0.9
0.7
0.8
0.1
0.1
0.1
0.1
0.1
Lase
1976
1977
1978
1979
1980
4
37
62
60
7
60
2,350
10,050
9,717
11,517
50
205
386
536
311
T
133
533
367
267
0
100
76
114
22
1.4
1.3
1.6
1.4
1.4
0.4
0.1
0.2
1.4
0.1
Lode
1976
1977
1978
1979
1980
4
2
18
5
7
580
1,167
8,033
4,100
3,467
998
0
999
999
999
T
167
467
283
250
0
0
242
650
550
0.7
1.0
0.9
0.7
0.8
0.3
.0
0.1
0.1
0.1
Lohu2
1976
1977
1978
1979
1980
1
8
5
10
483
567
0
114
684
T
T
T
0
0
0
0.1
0.3
0.3
0.1
0.1
0.1
Lopu3
1976
1977
1978
1979
1980
9
7
10
20
3
540
250
1,700
3,200
667
251
48
900
644
0
T
T
17
100
T
0
0
0
20
0
0.2
0.3
0.4
0.3
0.3
0.1
0.1
0.1
0.1
.0
Magr3
1976
1977
1978
1979
1980
2
5
10
12
38
50
67
883
833
4,500
50
33
539
338
387
T
T
83
33
250
0
0
0
0
47
0.9
1.1
2.1
1.6
2.1
0.7
0.5
0.1
0.2
0.1
Mito
1976
1977
1978
1979
1980
12
8
12
7
15
480
283
1,433
833
817
246
166
525
617
172
T
T
17
T
T
0
0
0
0
0
0.1
0.3
0.3
0.5
0.5
0.1
0.1
0.1
0.1
0.1
Soas
1976
1977
1978
1979
1980
10
3
8
5
8
130
50
367
50
167
21
50
163
0
77
T
17
33
T
T
0
0
0
0
0
0.1
1.7
1.6
0.8
1.0
0.1
1.6
0.4
0.3
0.3
.0
.0
continues
USDA Forest Service Res. Paper PSW-RP-239. 1999.
9
Table 33, continued
Vegetation
category
Annuals
and
biennials
Perennials
Species
abbrev.
Year
Freq.
Density
Cover
Pct
Plants/acre
Value
SE
Value
Height
Ft2/acre
SE
Ft
Value
SE
Stvi2
1976
1977
1978
1979
1980
7
18
12
23
850
500
250
3,533
762
100
55
999
133
50
T
200
100
50
0
0
1.6
1.5
1.7
2.4
0.7
0.2
0.2
0.4
Trdu
1976
1977
1978
1979
1980
3
2
2
33
17
17
0
0
0
T
T
T
0
0
0
1.4
1.0
2.2
0.1
.0
.0
Trci
1976
1977
1978
1979
1980
1
3
10
217
0
350
T
T
0
0
0.2
0.3
-
Viam
1976
1977
1978
1979
1980
44
48
53
48
47
2,610
5,183
10,000
3,467
7,450
104
262
408
217
433
10
317
233
117
400
0
46
29
24
99
0.2
0.4
0.3
0.6
0.7
0.1
0.1
0.1
0.1
0.1
Vilo2
1976
1977
1978
1979
1980
11
10
17
7
7
170
117
500
183
233
31
17
86
55
65
T
T
T
T
T
0
0
0
0
0
0.1
0.2
0.4
0.2
0.4
0.1
0.1
0.1
0.1
0.1
Aggr
1976
1977
1978
1979
1980
6
7
8
12
38
60
67
233
200
1,800
0
33
71
57
80
T
T
17
33
133
0
0
0
0
14
0.7
0.8
1.3
1.3
1.3
0.6
0.1
0.2
0.1
0.1
Appu
1976
1977
1978
1979
1980
2
2
3
2
3
20
67
83
17
83
0
0
150
0
150
10
17
T
T
17
0
0
0
0
0
0.2
0.5
0.6
0.3
0.8
.0
.0
0.1
.0
0.4
Asra
1976
1977
1978
1979
1980
8
7
12
12
13
220
133
417
800
317
105
100
157
443
38
10
T
67
33
33
0
0
33
0
0
0.6
0.8
1.4
0.8
1.1
0.1
0.2
0.3
0.1
0.3
Capr5
1976
1977
1978
1979
1980
5
7
33
100
0
50
T
T
0
0
0.6
1.6
0.3
0.2
Coar11
1976
1977
1978
1979
1980
2
5
150
167
350
0
T
T
0
0
0.4
0.6
-
.0
.0
.0
0.2
continues
10
USDA Forest Service Res. Paper PSW-RP-239. 1999.
Table 33, continued
Vegetation
category
Perennials
Species
abbrev.
Year
Freq.
Density
Cover
Pct
Plants/acre
Value
SE
Value
Height
Ft2/acre
SE
Ft
Value
SE
Dica14
1976
1977
1978
1979
1980
2
2
5
5
30
17
50
67
50
0
0
33
T
T
T
T
0
0
0
0
0.2
0.9
1.6
1.2
0.1
.0
0.1
0.1
Erla6
1976
1977
1978
1979
1980
2
2
17
50
0
0
T
T
0
0
0.5
1.3
-
Frve
1976
1977
1978
1979
1980
6
2
7
2
180
117
100
117
97
0
29
0
T
T
T
T
0
0
0
0
0.2
0.2
0.3
0.2
0.1
.0
0.1
.0
Gabo
1976
1977
1978
1979
1980
10
20
23
200
417
450
37
47
34
30
67
117
0
0
17
0.5
0.4
0.7
0.1
0.1
0.1
Hotr
1976
1977
1978
1979
1980
2
3
-
40
33
-
100
0
-
T
T
-
0
0
-
0.1
1.0
-
0.1
.0
-
Hyco3
1976
1977
1978
1979
1980
2
-
167
-
0
-
33
-
0
-
2.3
-
-
Hyra3
1976
1977
1978
1979
1980
3
7
15
22
260
67
400
1,400
717
0
107
124
T
17
17
T
0
0
0
0
0.1
0.9
0.9
0.7
0.1
0.1
0.1
0.1
Irha
1976
1977
1978
1979
1980
18
5
8
25
12
280
67
133
300
167
180
33
40
11
30
T
T
T
83
17
0
0
0
0
0
0.3
0.5
0.5
0.7
0.4
0.1
0.1
0.1
0.1
0.1
Osch
1976
1977
1978
1979
1980
2
17
0
T
0
0.5
0.1
Poco4
1976
1977
1978
1979
1980
4
3
7
7
2
90
67
83
200
17
48
100
25
200
0
T
T
T
17
T
0
0
0
0
0
0.2
0.4
0.5
0.5
0
0.1
0.1
0.1
0.1
.0
.0
.0
.0
-
continues
USDA Forest Service Res. Paper PSW-RP-239. 1999.
11
Table 33, continued
Vegetation
category
Perennials
Species
abbrev.
Year
Freq.
Density
Cover
Pct
Plants/acre
Value
SE
Value
Height
Ft2/acre
SE
Ft
Value
SE
Pogl9
1976
1977
1978
1979
1980
5
10
10
12
13
80
283
467
550
450
40
48
102
111
169
T
33
33
67
83
0
0
0
0
25
0.2
0.9
0.5
1.0
0.9
0.1
0.2
0.1
0.2
0.2
Sagr5
1976
1977
1978
1979
1980
1
2
2
-
40
17
17
-
0
0
0
-
T
T
T
-
0
0
0
-
1.5
0.2
0.6
-
0.2
.0
.0
-
Sima2
1976
1977
1978
1979
1980
30
20
33
23
23
980
900
1,067
867
517
75
125
55
113
41
20
183
233
150
83
0
15
24
58
25
0.1
1.1
0.8
0.7
0.9
0.1
0.1
0.1
0.1
0.2
Take
1976
1977
1978
1979
1980
4
3
3
70
33
50
48
0
50
T
T
T
0
0
0
0.4
0.7
0.8
0.2
0.2
0.2
Trla6
1976
1977
1978
1979
1980
14
20
30
23
47
770
783
2,967
2,133
6,467
241
115
156
277
268
T
T
50
50
67
0
0
0
0
0
0.1
0.2
0.2
0.2
0.3
0.1
0.1
0.1
0.1
0.1
Unkn
1976
1977
1978
1979
1980
1
2
2
10
17
17
0
0
0
T
T
T
0
0
0
0.2
0.4
0.3
0.1
.0
.0
1976
1977
1978
1979
1980
17
20
7
7
1,100
1,983
2,383
900
327
290
999
999
217
150
500
250
98
18
409
650
2.7
1.8
3.1
2.9
0.1
0.3
0.1
0.4
Bror2
1976
1977
1978
1979
1980
8
5
13
23
1
170
267
1,167
2,467
1,167
99
233
458
285
446
10
33
83
300
133
0
0
67
69
41
0.8
2.5
2.1
2.6
3.5
0.1
0.1
0.4
0.2
0.2
Casp
1976
1977
1978
1979
1980
23
23
28
17
22
1,000
1,100
583
350
333
112
145
41
47
27
20
83
100
117
100
0
33
29
24
0
0.5
1.0
1.1
1.2
1.1
0.1
0.2
0.1
0.1
0.2
Elgl
1976
1977
1978
1979
1980
3
15
12
57
33
3,817
1,950
8,400
0
999
541
319
T
267
150
800
0
260
0
77
1.6
2.1
3.1
2.8
1.3
0.5
0.4
0.3
Graminoids Brsp
continues
12
USDA Forest Service Res. Paper PSW-RP-239. 1999.
Table 33, continued
Vegetation
category
Species
abbrev.
Graminoids Femy2
Bracken
fern
Year
Freq.
Density
Cover
Pct
Plants/acre
Value
SE
Value
Height
Ft2/acre
SE
Ft
Value
SE
1976
1977
1978
1979
1980
2
2
7
8
17
750
500
317
0
0
307
73
T
17
17
T
0
0
0
0
0.4
1.2
1.0
0.9
.0
.0
0.2
0.1
Feoc
1976
1977
1978
1979
1980
5
5
5
12
500
300
1,550
4,917
379
451
999
999
100
17
267
583
58
0
219
369
2.5
2.9
2.6
2.5
0.4
0.4
0.2
0.3
Sihy
1976
1977
1978
1979
1980
2
2
-
17
100
-
0
0
-
T
T
-
0
0
-
0.5
1.0
-
-
1976
1977
1978
1979
1980
47
57
65
47
52
3,760
10,233
10,333
8,133
7,883
73
173
265
248
229
350
1,367
1,517
1,283
1,067
12
34
107
39
49
0.8
1.0
1.0
10
1.1
Ptaq
-
.0
.0
0.1
0.2
0.3
0.1
0.1
Table 4—
4—Top four plant species having largest number (density), best horizontal development (foliar cover), and best vertical development
(height), Challenge Experimental Forest, 1976-1980
Year
Rank
Density
Cover
Height
1976
1
2
3
4
Ptaq
Cein3
Viam
Todi
Ptaq
Civu
Lide3
Todi
Sagr5
Lide3
Lase
Clrh
1977
1
2
3
4
Civu
Ptaq
Viam
Arvi4
Civu
Ptaq
Cein3
Arvi4
Coca5
Brsp
Lide3
Feoc
1978
1
2
3
4
Civu
Ptaq
Lase
Viam
Civu
Cein3
Ptaq
Arvi4
Feoc
Bror2
Elgl
Magr3
1979
1
2
3
4
Lase
Ptaq
Hygl2
Lode
Cein3
Arvi4
Ptaq
Cele
Lide3
Elgl
Brsp
Feoc
1980
1
2
3
4
Hygl
Lase
Elgl
Ptaq
Arvi4
Cein3
Ptaq
Lide3
Lide3
Bror2
Cein3
Bapi
USDA Forest Service Res. Paper PSW-RP-239. 1999.
13
Average dominant height, which is a measure of vertical development, was expressed best by
tanoak (Lide3) in 1976 and a few plants of annual species that grew tall in the absence of competition.
Height development from 1977 through 1979 was notable for a species of brome (Brsp), western fescue
(Feoc), Orcutt’s brome (Bror2), and blue wildrye (Elgl)—all perennial grasses—whose strategy was to
grow tall at an early age. The tallest species in 1980 were a mixture of hardwood (Lide3), graminoid
(Bror2), and such shrubs as deerbrush (Cein3) and coyote brush (Bapi). Of particular note was tanoak,
which ranked among the four tallest species in 4 of the 5 years in the study.
One factor that can influence the density and horizontal development of plant species in newly
developed openings is damage from biotic and abiotic agents. The only agent in this study that had a
noticeable effect was deer. Browsing damage in fall 1976 to the young plants was severe. Species like
deerbrush (Cein3) and California black oak (Quke) were browsed to nubs of naked stems, and larger
perennials like dwarf checkermallow (Sima2) and gland cinquefoil (Pogl9) were virtually stripped of all
green material. Most remarkable was that species like western bracken fern (Ptaq), Sierran mountain
misery (Chfo), whiteleaf manzanita (Arvi4), Pacific poison oak (Todi), rainbow iris (Irha), and
smoothleaf raspberry (Rugl), which are scarcely touched when older, were severely browsed. Even they
became palatable, probably because of their high nutrient content—a response to the large amount of
soil nitrogen available just after site preparation. Many plants of American vetch (Viam) were pulled
out of the ground. Browsing declined rapidly in 1977 and rated only as occasional thereafter.
Categories of Species
Conifers
Conifer seedlings originated from seeds blown in from nearby trees in fall 1976. The most abundant
species was ponderosa pine (PipoP). Mean conifer seedling density decreased from 551 to 417 per acre
during the study (fig. 3). Horizontal and vertical development were slow, with values of 33 ft2 per acre
(fig. 4) and 0.7 foot (fig. 5), respectively, at the end of the study.
600
500
Plants/acre
400
300
200
1976
1977
1978
Year
Hardwoods
_
_
_
0
_
100
1979
1980
Conifers
Figure 3—Density of hardwoods and conifers, Challenge Experimental Forest, 1976-1980. Standard errors for
hardwoods ranged from 48 to 125 plants per acre in a given year; for conifers, from 80 to 153 plants per acre.
14
USDA Forest Service Res. Paper PSW-RP-239. 1999.
1,200
1,000
Cover (ft2/acre)
800
600
400
1976
1977
_
_
_
0
_
200
1978
Year
1979
Hardwoods
1980
Conifers
Figure 4—Foliar cover of hardwoods and conifers, Challenge Experimental Forest, 1976-1980. Standard errors for
hardwoods ranged from 28 to 383 ft2 per acre in a given year; for conifers, from 5 to 22 ft2 per acre.
4
Height (ft)
3
2
1976
_
_
_
0
1977
_
1
1978
Year
Hardwoods
1979
1980
Conifers
Figure 5—Height of hardwoods and conifers, Challenge Experimental Forest, 1976-1980. Standard errors for
hardwoods ranged from 0.3 to 2.0 feet in a given year; for conifers, from 0 to 0.1 foot.
USDA Forest Service Res. Paper PSW-RP-239. 1999.
15
Hardwoods
Hardwoods initially were from two kinds of sprouts: root-crown sprouts that originated from dormant
buds on the burl and seedling-sprouts. Seedling-sprouts, most of which were tanoak (Lide3), are
resprouts of seedlings in the seedling bank that survived the harvest and site preparation, died back to
groundline, and resprouted. Additional recruits to the hardwood category were by seedlings from
acorns and berries. The few Pacific madrone (Arme) plants present in 1977-1978 were all from seed.
The major contributor to the hardwood category was tanoak, which at the end of the study, was
developing rapidly and forming tall, wide clumps of stems. During the study, hardwood density
increased 73 percent (fig. 3), foliar cover expanded more than ten times (fig. 4), and height increased
more than five times (fig. 5).
Shrubs
Plants from almost all species in this category were from seed. The one exception was Pacific poison
oak (Todi), which originated from plants that escaped harvest and site preparation. Mean shrub
density was characterized by a relatively high initial density (9,710 plants per acre) and a steady
increase to 14,351 plants per acre at the end of the study (fig. 6), for a 48 percent gain. Foliar cover of
shrubs expanded from 310 ft2 per acre at the beginning to 10,181 ft2 per acre at the end of the study for
over a thirtyfold increase (fig. 7). Mean shrub height increased from 0.3 feet in 1976 to 1.6 feet in 1980
for more than a fivefold increase (fig. 8). Major contributors to these gains were whiteleaf manzanita
(Arvi4), deerbrush (Cein3), Sierran mountain misery (Chfo), and Pacific poison oak (Todi). Deerbrush
in particular was developing rapidly and forming large clumps of tall stems.
Annuals and Biennials
Plants in this category originated mostly from windblown seeds or from dormant seeds in the soil.
Some species, notably bull thistle (Civu), developed first from windblown seed and then from seed of
the ensuing plants. In contrast, plants of American vetch (Viam) originated from buried seed with
subsequent recruitment from buried seed and seed produced by the plants. In terms of huge numbers
of plants present soon after disturbance, both species were equally successful.
The classical buildup and decline of a biennial invader was illustrated by bull thistle (Civu),
whose seeds blow in on the wind, germinate in the fall, result in plants that overwinter as a rosette,
70,000
60,000
Plants/acre
50,000
40,000
30,000
20,000
10,000
1976
Shrubs
1977
Annuals
1978
Year
Perennials
_
_
_
_
0
1979
Graminolds
1980
Fern
Figure 6—Density of five categories of vegetation, Challenge Experimental Forest, 1976-1980. Standard errors for
shrubs ranged from 350 to 421 plants per acre in a given year; for annuals, from 197 to 1,268; perennials, from 74 to
360; for graminoids, from 92 to 489 plants per acre.
16
USDA Forest Service Res. Paper PSW-RP-239. 1999.
12,000
Cover (ft2/acre)
10,000
8,000
6,000
4,000
2,000
0
1976
Shrubs
1977
1978
Year
1979
Annuals
Perennials
1980
Graminolds
Fern
Figure 7—Foliar cover of five categories of vegetation, Challenge Experimental Forest, 1976-1980. Standard errors
for shrubs ranged from 11 to 443 ft2 per acre in a given year; for annuals, from 7 to 144; perennials, from 2 to 17; and
for graminoids, from 5 to 128 ft2 per acre.
2.5
Height (ft)
2
1.5
1
1976
Shrubs
_
_
_
0
1977
Annuals
_
0.5
1978
Year
1979
Perennials
Graminolds
1980
Fern
Figure 8—Height of five categories of vegetation, Challenge Experimental Forest, 1976-1980. Standard errors for
shrubs ranged from 0.1 to 0.3 foot in a given year; for annuals, from 0.1 to 0.2; perennials, from 0.1 to 0.2; and for
graminoids, from 0.2 to 0.4 foot.
USDA Forest Service Res. Paper PSW-RP-239. 1999.
17
bolt in early spring, grow tall, produce thousands of seeds, and die. The population peaked in 1977
and 1978, and then typically collapsed (table 3) (McDonald and Tappeiner 1986, Randall 1990).
Plants of other species from all but the hardiest of propagules had a difficult time becoming established
in these years (fig. 9).
The density of annuals and biennials began with fairly high numbers, increased almost fivefold by
the end of 1977, and again increased (67 percent) in 1978 (fig. 6). Almost a 39 percent decrease
characterized 1979 as the mean density of bull thistle (Civu), riverbar birdfoot trefoil (Lode), and
American vetch (Viam) fell dramatically. Over 60,000 plants per acre were present in this category in
1980 due largely to increases in density by many species, including Epilobium paniculatum (Eppa2),
smooth catsear (Hygl2), prickly lettuce (Lase), grassy tarweed (Magr3), rod wirelettuce (Stvi2), and
American vetch (Viam). Foliar cover peaked in 1978 at 4,233 ft2 per acre and declined to 2,668 ft2 per
acre in 1980 (fig. 7). Mean height of annuals and perennials ranged from 0.4 feet to 1.2 feet during the
study (fig. 8).
Perennials
Most perennial species in this study originated from both seeds blown in on the wind or those from the
seedbank in the soil. For the first 4 years, density was dominated by dwarf checkermallow (Sima2) and
Trientalis latifolia (Trla6) and then in 1980 by Trla6, bigflower agoseris (Aggr), and hairy catsear
(Hyra3) (fig. 6). Dwarf checkermallow also was a major contributor to foliar cover during the first 4
years, with bigflower agoseris and Bolander’s bedstraw (Gabo) contributing most in 1980 (fig. 7). The
tallest perennials were composed of different species almost every year and ranged from 0.1 to 1.5 feet
tall in year 1 to 0.3 to 1.6 feet in 1980 (fig. 8).
Graminoids
When the study began, the graminoids consisted of one grass (Orcutt’s brome [Bror2]) and one sedge
(Casp). Together, their density was 1,170 plants per acre. This value increased steadily, so that by the
end of the study the density of the six graminoids was more than 16,000 per acre (fig. 6). Foliar cover
likewise increased steadily from 30 ft2 per acre to 1,866 ft2 per acre at the study’s end (fig. 7). Mean
height increased from 0.6 to 2.3 feet during the study (fig. 8).
Bracken Fern
Western bracken fern (Ptaq) is found from the Arctic Circle to the Equator and is common on every
continent (Minore 1966). It is particularly adapted to disturbed areas, but retains a presence in all
stages of succession. The density of this species began fairly high (3,760 stems per acre), increased
dramatically to more than 10,200 stems per acre in 1977, flattened out in 1978 (10,333 per acre), and
then declined the next 2 years (fig. 6). At the end of the study, bracken fern density was 7,883 stems per
acre. Foliar cover began at 350 ft2 per acre, increased through three growing seasons to 1,517 ft2 per
acre, and then declined to 1,067 ft2 per acre at the end of the study (fig. 7). Mean height began at 0.8
foot and increased slowly to 1.1 feet at the study’s end (fig. 8).
The Plant Community
Density of all plant species was 24,860 plants per acre after one growing season, increased through the
third growing season to 91,631 plants per acre, declined the fourth season to 71,167 per acre, and then
increased to 112,408 plants per acre at the end of the study. Foliar cover increased each year from 950
ft2 per acre to 17,433 ft2 per acre at the study’s end.
When each category of species is presented for each descriptive characteristic and illustrated as a
proportion of the total of that characteristic each year, the changing nature of the plant community is
more apparent (figs. 10, 11).
On the virtually bare ground representative of the study area in fall 1976, the shrubs, annuals and
biennials, and ferns dominated in terms of number of plants (fig. 10). By 1977, more than half of all the
plants in the total community were annuals and biennials—a condition that continued throughout the
study. Another category whose members increased in density throughout the study was the graminoids.
Density of the conifers and hardwoods was very low compared to the other categories of vegetation.
Density of shrubs and bracken fern declined proportionally as components of the plant community.
In terms of foliar cover (fig. 11), the initial values were largest for bracken fern, shrubs, and
annuals and perennials, and continued as such for the next 2 years. In 1979, foliar cover of the
18
USDA Forest Service Res. Paper PSW-RP-239. 1999.
Figure 9—With over 20,000 thistles
per acre using available resources,
most other plant species would find
it difficult to become established.
Challenge Experimental Forest, 1977.
F
P
O
graminoids became larger than that of the fern. The large increase in shrub cover was also notable in
1979 when it amounted to more than 59 percent of that in the total plant community—a proportion
that continued in 1980. In the last 2 years of the study, foliar cover of the hardwoods and graminoids
was increasing, and that of the perennials was low and virtually stable. Foliar cover of the annuals and
biennials was characterized by a buildup in 1977 and 1978, followed by a major decline in 1979, and a
slight increase in 1980. The proportion of foliar cover contributed by the conifers was very low.
Of the species present during the study, 31 percent never had more than 0.5 ft 2 of cover.
Conversely, after the first year, less than 25 percent of the species present contributed over 90 percent
of foliar cover.
In terms of height, and by definition “average dominant height,” all categories of vegetation were
increasing over time except the perennials (fig. 8). Average dominant height, of course, is lowered by
shorter new recruits, especially in instances where only one or two plants are present. Although many
species indicated a propensity to grow tall during the study (table 3), only one category of vegetation,
the graminoids, consistently dominated over all others in terms of vertical development (fig. 8). The
graminoids were also among the four tallest species present in 1977 through 1980 (table 4, fig. 8).
Indeed, in 1978 and 1979, three of the four tallest species in the study were graminoids. Although the
graminoids were taller, their height was leveling off (fig. 8). In contrast, the trend of shrub height not
only was increasing, but at an increasing rate (fig. 8).
Discussion and Conclusions
Before harvest, the study area was covered with a dense mixture of conifer and hardwood trees of many
sizes and age classes, including seedlings and saplings of shade tolerant species. The soil surface was
mostly a dense carpet of needles and leaves with western bracken fern (Ptaq) and Pacific poison oak
(Todi) scattered throughout. Sierran mountain misery (Chfo) also was present in scattered patches.
After harvest and site preparation, the study area consisted of mostly bare ground with small tanoak
(Lide3) and California black oak (Quke) stumps and residual plants of Pacific poison oak and Sierran
mountain misery above ground and western bracken fern (Ptaq) below ground, along with thousands
of dormant seeds in the soil.
These species, plus many more with plants from buried seeds and seeds that blew in on the wind,
quickly invaded the study area. By the end of the first growing season, several categories of vegetation,
including shrubs, annuals, ferns, and grasses, were well represented. None of these categories contained
less than 7,800 plants per acre or a cover of less than 1,000 ft2 per acre at the end of the study. The
hardwoods also had a foliar cover of over 1,000 ft2 per acre.
USDA Forest Service Res. Paper PSW-RP-239. 1999.
19
Figure 10—Proportional changes in
plant density for the various
categories of vegetation. Challenge
Experimental Forest, 1976-1980.
CONIFERS
HARDWOODS
1976
CONIFERS
HARDWOODS
1977
FERN
FERN
GRAMINOIDS
SHRUBS
GRAMINOIDS
SHRUBS
PERENNIALS
PERENNIALS
ANNUALS & BIENNIALS
ANNUALS & BIENNIALS
1978
FERN
CONIFERS
HARDWOODS
SHRUBS
1979
CONIFERS
HARDWOODS
FERN
SHRUBS
GRAMINOIDS
GRAMINOIDS
PERENNIALS
PERENNIALS
ANNUALS & BIENNIALS
ANNUALS & BIENNIALS
1980
FERN
CONIFERS
HARDWOODS
SHRUBS
GRAMINOIDS
PERENNIALS
ANNUALS & BIENNIALS
Figure 11—Proportional changes in
foliar cover for the various categories
of vegetation. Challenge Experimental
Forest, 1976-1980.
CONIFERS
HARDWOODS
1976
CONIFERS
HARDWOODS
1977
FERN
SHRUBS
FERN
SHRUBS
GRAMINOIDS
PERENNIALS
GRAMINOIDS
PERENNIALS
1978
ANNUALS & BIENNIALS
FERN
ANNUALS & BIENNIALS
CONIFERS
HARDWOODS
1979
FERN
CONIFERS
HARDWOODS
GRAMINOIDS
GRAMINOIDS
SHRUBS
PERENNIALS
PERENNIALS
ANNUALS & BIENNIALS
ANNUALS & BIENNIALS
SHRUBS
1980
FERN
CONIFERS
HARDWOODS
GRAMINOIDS
PERENNIALS
ANNUALS & BIENNIALS
SHRUBS
20
USDA Forest Service Res. Paper PSW-RP-239. 1999.
The categories of vegetation that were poorly represented at the end of the study were the conifers
and the perennials. The conifers, which were represented almost entirely by ponderosa pine (PipoP),
had a frequency value that indicated a clumpy distribution (table 3). They also got a late start with none
present until 1977 (table 3). Thus, they began life with heavy competition in many of the most
favorable microsites. Many died. Ponderosa pine seedlings that were alive at the end of the study were
those that occupied small areas free of shrubs, clumps of hardwoods, or high densities of annuals and
graminoids. The short height of the pines also suggests that some were overtopped and growing
slowly. More will die, but those that remain will eventually dominate.
The severe browsing of some shrubs by deer early in the study may actually have aided their
development and dominance potential. Deerbrush and whiteleaf manzanita (Cein3 and Arvi4) seemed
to have benefited by damage to the main stem, which led to the development of multiple stems at an
early age, and increased their potential for higher foliar cover.
The diversity and development of the perennials in this plant community was puzzling. With 21
species present during the study, and a trend of increasing number of species, this category of plants
was well represented. However, their contribution to the community in terms of density and cover was
relatively small. Not only was their density value at the end of the study only 11 percent of the
community and their cover value only 4 percent, but the trend in density was that of a slow increase,
and cover was flat. Mean height was actually declining. Perhaps the strategy of the perennials is to first
establish a presence, and then await a more suitable environment. Perhaps a condition of being
perennial in the environment of this study is to develop better later. Antos and Halpern (1997) found that
perennials in a recent clear-cutting in western Oregon had greater root development than annuals, suggesting
that this condition probably contributed to their ascendency later in the successional sequence. Previous
work on the Challenge Experimental Forest has shown a high proportion of perennials becoming established
over a longer timespan in a more shady environment (McDonald and Reynolds 1999).
Although the total number of species increased at the end of the study, this gain was limited to the
annuals and perennials. Future increases may be tempered, however, by several factors. The resident
species already are numerous and of many categories, plant density is high, and the height of tanoak
(Lide3) and the shrubs is exploding. Certainly the supply of available resources such as light, nutrients,
and water is diminishing. The resident species probably are inhibiting invasion and establishment by
preempting available space or more specifically by occupying the habitable microsites. This was
readily seen in this study in areas of differing microrelief. Depressions often were occupied by many
plants of several species, while nearby mounds were barren. Resident species also modified the
environment (more shade for example), which in turn inhibited the germination of seeds and the
development of plants that became present.
Sousa (1984) noted that the resources made available by a disturbance are soon exhausted by new
colonists and regrowth of survivors. Further growth often is curtailed. At the end of the study, total
foliar cover was 17,433 ft2 per acre or 40 percent. Plainly, space was available for additional horizontal
development. But, although increasing, the rate of increase decreased each year from 1977 through
1980. Thus, on a site of high quality, such as this, growth may be more slowed than curtailed, at least
during the first 5 years.
Although it is impossible to establish a definitive successional progression in only 5 years, some
early trends are noteworthy. Tanoak (Lide3) and ponderosa pine (PipoP) will be the most abundant
trees, and whiteleaf manzanita (Arvi4) and deerbrush (Cein3) will be the most abundant and dominant
shrubs. Tanoak and the shrubs will continue to expand rapidly in foliar cover and height and dominate
the plant community for years to come. Ponderosa pine will be scattered in small groups and as single
trees. The annuals and graminoids will be increasingly relegated to small openings among the trees and
shrubs, and the shade-tolerant perennials likely will increase in numbers and density and reside in both sun
and shade environments. Western bracken fern will be present in various amounts almost everywhere.
Consequently, the mode or process of succession is best characterized as “modified”
environmental succession. The dominant species of the near future will be those whose regeneration
strategies result in early dominance. Sprouting shrubs and hardwoods with burgeoning foliar cover
and height are good examples. As the crowns of trees and shrubs close, and the high density of the
annuals and graminoids decrease, more shade-tolerant conifers such as Coast Douglas-fir (PsmeM)
and incense-cedar (Lide) and other tolerant perennials and graminoids will become established. Thus,
succession will occur through environmental modification. It is not classical replacement of one stage
of species by another stage, however, because the first stage will be present for many years. Species of
random origin, especially those from windblown seeds, will not be a major part of the understory plant
USDA Forest Service Res. Paper PSW-RP-239. 1999.
21
community. Plants from the seedbank in the soil will not be a major part of this community either.
However, they will have accomplished their mission because the storehouse in the soil will have been
replenished, and they once again will be poised to take advantage of another disturbance.
As ecology becomes more important in forestry, knowledge about plant species and plant
communities that develop naturally or after a deliberate manipulation is increasingly needed.
Manipulation could be for a variety of reasons: to create a future forest, to provide an economic crop, to
grow plants whose seeds or browse would be critical to wildlife, or simply to have present a broad base
of species and age classes and thus be able to provide amenities and commodities that will be needed in
the future. Data from studies such as this will be invaluable for accomplishing such goals.
References
Antos, Joseph A.; Halpern, Charles B. 1997. Root system differences among species: implications for early successional changes
in forests of western Oregon. American Midland Naturalist 138: 97-108.
Clements, F.E. 1916. Plant succession: an analysis of the development of vegetation. Carnegie Institute Washington Publication
242; 512 p.
Daubenmire, R.F. 1968. Plant communities: a textbook on plant synecology
synecology. New York: Harper and Row; 300 p.
forests. Presented before the subcommittee on forests and
Dombeck, Mike. 1997. Concerning criteria for managing healthy forests
forest health, U.S. House of Representatives. March 18, 1997; 13 p.
Egler, F.E. 1954. Vegetation science concepts: I. Initial floristic composition, a factor in old-field vegetation development.
Vegetatio 4: 412-417.
Gordon, Donald T. 1979. Successful natural regeneration cutting in California true firs. Res. Paper PSW-140. Berkeley, CA:
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Grime, J.P. 1979. Plant strategies and vegetation processes
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22
USDA Forest Service Res. Paper PSW-RP-239. 1999.
The Forest Service, U.S. Department of Agriculture, is responsible for Federal
leadership in forestry.
It carries out this role through four main activities:
• Protection and management of resources on 191-million acres of National Forest System
lands
• Cooperation with State and local governments, forest industries, and private landowners
to help protect and manage non-Federal forest and associated range and watershed
lands
• Participation with other agencies in human resource and community assistance programs
to improve living conditions in rural areas
• Research on all aspects of forestry, rangeland management, and forest resources
utilization.
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• Represents the research branch of the Forest Service in California, Hawaii, American
Samoa, and the western Pacific.
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United States
Department
of Agriculture
Forest Service
Pacific Southwest
Research Station
Research Paper
PSW-RP-239
Diversity, Density, and Development of
Early Vegetation in a Small Clear-cut
Environment